It is highly required in a Long Term Evolution (LTE) system to position a terminal. At present, there are the following several general methods for positioning a terminal.
In a first method based upon positioning with a Global Position System (GPS), a GPS device is installed in a terminal to thereby acquire and report to the system the current position of the terminal.
In a second method based upon positioning with a system cell, a rough position of a terminal can be acquired by referring to a station address of a current serving cell of the terminal because the station addresses of serving cells are typically known during deployment of a communication system.
In a third method based upon positioning with Observed Time Difference of Arrival (OTDOA), a terminal measures concurrently transmission time differences of more than three nearby cells and multiplies the transmission time differences by transmission velocity (the velocity of light c) to derive distance differences and hereby plane curve equations of the position of the terminal, and the position of the terminal can be derived from an intersection of curves corresponding to the plane curve equations of the cells.
Among the foregoing three methods, the first method with relatively high precision of positioning has to rely upon the expensive GPS device, and this method is costly to implement and relies upon the required capability of the terminal to receive a GPS signal; the second method has too low precision of positioning, especially in a macro cell with a large coverage area of a base station; and the third method with relatively high complexity of measurement requires concurrent measurement and reporting by the terminal of the transmission time differences of three nearby cells, which may result in significant signaling overhead, furthermore, the terminal centered in a cell may measure a surrounding cell with a considerable error due to an interference and a signal strength.